The present invention concerns an apparatus for attaching a ship rudder with a conical opening to a rudder shaft, a rudder shaft, a ship rudder with a conical opening in the rudder and a method for attaching a rudder shaft to a ship rudder.
During attachment of a ship rudder with a conical connection between the rudder and the rudder shaft, it has turned out that the current solutions result in limitations in optimisation of rudder design with respect to hydrodynamics, propulsion efficiency, installation processes and production costs.
Today, normally are rudders attached to the rudder shaft by means of a conical connection, where a hydraulic pressure is applied between the rudder and the rudder shaft in the conical surface and hydraulic pressure is applied to an assembly tool, normally designed as a nut with an internal hydraulic piston (hydraulic nut). The hydraulic nut is assembled to the lower part of the rudder shaft and pulls the rudder shaft down into the rudder. It is necessary with access to the nut through one or several openings in the rudder. When the assembly process has been performed, the assembly tool or nut is locked towards the rudder shaft and then acts as a safeguard against the rudder falling off if the conical connection should fail. The opening or openings in the rudder are thereafter closed with one or several covers. This solution is however unfavourable, in particular with large rudder shaft diameters, because the hydraulic nut becomes large and bulky, and is vulnerable to damages. Furthermore the opening or openings in the rudder for access to the hydraulic nut leads to unfavourable stress concentrations, and reduces the material cross section in this section of the rudder. This reduces the physical strength of the rudder, and this has to be compensated with a more bulky and heavy structure in the rudder. This again leads to increased production costs. Furthermore the rudder must physically include space for the hydraulic nut, and the thickness of the rudder may be dictated by this space. This poses further limitations for optimisation of the rudder design with respect to hydrodynamics and propulsion efficiency.
In JP 8-34397 it is shown a structure for assembly of a rudder and a rudder shaft with a conical portion and a system for hydraulic tightening.